Not applicable.
Not Applicable.
1. Field of the Invention
The invention relates to a bushing arrangement and method for passing cable through an opening in a wall, plating, partition and the like, such as a bulkhead of a ship, for example while providing protection against electromagnetic overtension and/or interference. Hereinafter, the term xe2x80x9cwallxe2x80x9d will be used for the sake of simplicity, while this term is understood to include other partitions as well.
2. Description of the Related Art
A bushing arrangement is disclosed in Dutch patent application no. 1011718 in the name of the present applicant. The bushing arrangement that is disclosed therein consists of a steel bushing fitted in a wall opening, through which a number of single-core or multiple-core steel bushing fitted in a wall opening, through which a number of single-core or multiple-core cables are passed. The cables are stripped of their sheathing along a suitable part of their length, so that said cables can locally come into electrically conductive contact with their environment. The longitudinal parts of the cables are then embedded in an electrically conductive moulding paste so as to effect electrical conduction between the cables and the bushing arrangement, after which the wall opening is filled up with a suitable sealing compound. A rubber hose member may be fitted round each cable before the moulding paste is provided, while any remaining space in the wall opening will be filled with the similar hose members. One drawback of the bushing arrangement that is disclosed in the aforesaid Dutch patent application is the fact that it has become apparent in practice that in some cases the moulding paste exhibits a relatively high electrical resistance value, in the order of about 100-100 Ohm, after curing. In particular this means that the degree to which electricity can flow away to earth or ground via the moulding paste has decreased considerably, which has an adverse effect on the extent of protection that is provided against electromagnetic overtension. The same applies, mutatis mutandis, as regards (the protection against) electromagnetic interference.
The object of the invention is to improve the bushing arrangement that is known from the prior art, in the sense that there is proposed a high-grade fire resistant, gastight and liquid-tight bushing arrangement which is furthermore optimally protected against electromagnetic overtension and/or interference.
In order to accomplish that objective, a bushing arrangement of the kind referred to in the introduction is characterized in that the bushing arrangement includes an electrically conductive tape which is in contact with an electrically conductive cable shielding of a one cable being passed through and which functions to earth the cable shielding.
Electrical installations and machines, which usually include highly sensitive components, for example for control and registration purposes, can easily experience interference caused by various external electromagnetic (em) fields and pulses. Such electromagnetic fields and pulses may have been generated by radar installations, thunderstorms, nuclear explosions and electrical equipment, for example. A measure that is frequently used in practice for reducing such interference is the provision of a steel structure which functions as a Faraday cage around the space that is intended for electronic equipment. Electrical cables that are passed into such a screened space can conduct undesirable electromagnetic fields and pulses into the electronic equipment, however. Such conduction will generally take place over the electrically conductive shielding (braid) of the respective cables that are passed through.
According to the invention, the external undesirable em fields and pulses will flow away to earth along the electrically conductive shielding of a cable being passed through, via the electrically conductive tape. In particular, the electrically conductive tape is at least partially wound round the electrically conductive cable shielding.
It is noted that within the framework of the invention the term xe2x80x9ccablexe2x80x9d is understood to include an electrically conductive conduit, tube, pipe or the like, for example a metallic tube or pipe, with the present tape being in electrically conductive contact therewith when operative.
In one preferred embodiment of a bushing arrangement according to the invention, the electrically conductive tape is wound around the electrically conductive cable shielding near one end, while it is in electrically conductive contact with an electrically conductive bushing housing (made of a metal, for example) that is fitted in the opening in the wall. In another preferred embodiment, the grounding of the electrically conductive cable shielding is effected by means of the electrically conductive tape by providing an electrically conductive material on at least one open side of the wall, which material is in electrically conductive contact with the tape. The electrically conductive material is at least substantially made up of several pieces of electrically conductive tape material, whether or not folded, which have been placed into the opening, and/or of several electrically conductive sleeves or hose members which have been placed into the opening, which hose members or sleeves preferably extend in the same direction as the cable being passed through.
In another preferred variant, the electrically conductive material is the graphite-containing moulding paste that is known from the aforesaid Dutch patent application no. 1011718.
In another preferred embodiment of a bushing arrangement according to the invention, the electrically conductive tape and/or the electrically conductive sleeve is/are substantially made of an electrically conductive rubber. The rubber has been made electrically conductive by chemical means, in particular through the addition thereto of carbon particles, preferably in the form of carbon black. In particular, the rubber is EPDM rubber, while the carbon particles are preferably concave shell-shaped, especially of the type xe2x80x9cKetjenblack ECxe2x80x9d 300J or 600 JD(trademark). These existing types of carbon black known under the commercial name of xe2x80x9cKetjenblackxe2x80x9d have a unique morphology in comparison with conventional types of carbon black, which renders them exceptionally suitable for the present electrically conductive application. The abbreviation EPDM stands for Ethylene/Propylene/Diene/Monomer. It is noted that also other elastomers or plastomers can be used as materials for the tape and the sleeves.
In another preferred embodiment of a bushing arrangement according to the invention, the electrically conductive tape is a metal tape. Preferably, the electrically conductive tape, rubber or metal, is flexible, that is, deformable, so that it can readily be passed along other cables that are passed through the bushing arrangement.
In another preferred embodiment of a bushing arrangement according to the invention, the electrically conductive tape has a contact width of at least about 20 mm, preferably about 40 mm. In the latter case, the tape is usually used for civil applications (attenuation factor xe2x88x9230 dB), while a contact width of more than 100 mm (attenuation factor xe2x88x9260 dB) can be used for military applications. By winding the present tape of such width around the electrically conductive cable shielding, an optimum electrically conductive contact is effected so as to prevent electromagnetic overtension and/or interference.
In another preferred embodiment of a bushing arrangement according to the invention, the remaining space in the wall opening is at least partially filled up with several fire resistant sleeves, which extend in the same direction as the cable being passed through. Each cable may be passed through one of the sleeves. The sleeves or hose members are preferably divided lengthways, so that, in the latter case, they can be fitted over the cables after the cables have been pulled through the bushing arrangement.
In another preferred embodiment of a bushing arrangement according to the invention, a heat resistant and/or liquid repellent (preferably expandable) putty is used in at least one open side of the wall opening for sealing the wall opening. The putty functions to enhance the gas tightness and liquid tightness of the present bushing arrangement.
The invention furthermore relates to a method for passing a cable through an opening in a wall while providing protection against electromagnetic overtension and/or interference, using a bushing arrangement according to the invention, characterized in that in use an electrically conductive tape is brought into contact with the electrically conductive shielding of the cable being passed through for the purpose of grounding it.